Re: [ATM] telescope vibrations

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> For a given tube length, if the length is reduced by a factor of two, what
> is the impact on the amplitude of wind induced vibrations, What is the
> impact on the frequency of wind induced vibrations, what is the impact on
> the duration of the vibrations for a impulse on the OTA ?

Reducing length, assuming that this reduces surface area exposed to force of 
wind proportionally, will result in a force 1/3 that of the full length. 
This means that 1/3 of the energy will be dumped into the telescope, causing 
similar reduction in amplitude and time to decay.  Since the moving parts 
are likely vibrating at their combined resonant frequency, I anticipate no 
change in this frequency.  If parts are sufficiently decoupled, and if a 
part is not excited enough with the reduced length, and if that part has a 
resonant frequency different from the rest of the moving parts, then the 
overall observed frequency will change.  Usually in this case, this mystery 
part will have a lower frequency, so the resulting frequency will be higher.

You can experiment a little bit by holding the tube assembly out the window 
while driving down the road - I've done this and it's worth seeing the 
reaction from the cows as you drive by on the country road <smile>.

Mel Bartels 

_______________________________________________
ATM mailing list http://www.atmlist.net/